Imaging catheter assembly with distal end inductive coupler and embedded transmission line

ABSTRACT

A catheter assembly includes an elongate catheter body having a proximal end and a distal end with a drive cable disposed therein, the drive cable having a proximal end and a distal end, and rotatable relative to the catheter body. A first electro-magnetic element is disposed proximate the distal end of the catheter, and a second electro-magnetic element disposed proximate the distal end of the drive cable and in electrical communication with an operative element mounted at the end of the drive cable, the first and second electro-magnetic elements forming an inductive coupler. The catheter assembly can include various other distal operative elements, which are in communication with corresponding proximal operative elements via transmission lines embedded within the wall of the catheter body.

This is a continuation of U.S. patent application Ser. No. 09/834,684filed on Apr. 13, 2001 and now U.S. Pat. No. 6,450,965, which is acontinuation of U.S. patent application Ser. No. 09/238,647, filed Jan.26, 1999, now U.S. Pat. No. 6,245,020, which is a continuation-in-partof U.S. patent application Ser. No. 09/013,463, filed Jan. 26, 1998, nowabandoned. The priority of the prior applications is expressly claimed,and the disclosures of the prior applications are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

The present invention pertains to catheter systems and, moreparticularly, to intraluminal catheter assemblies used in diagnostic andtherapeutic applications.

BACKGROUND

Intraluminal catheter assemblies are employed to diagnose and/or treatabnormalities within the human vasculature. A typical intraluminalcatheter assembly includes a distally mounted operative element, suchas, e.g., an ablation electrode, which is in electrical communicationwith a proximally located operative element, such as, e.g., an RFgenerator. Currently, intraluminal catheter assemblies include elongatecatheter bodies in which internal lumens are extruded for the purpose ofrouting transmission lines between the distally mounted operativeelement and the proximally located operative element.

Often, intraluminal catheter assemblies support multiple distallymounted operative elements, thereby providing the physician with asingle multi-functional platform. Because the radius of the catheterbody must be small enough to be transported through the vasculature,however, the size and number of internal lumens which can be extrudedthrough the catheter body becomes a critical factor, thereby limitingthe amount, combination and/or performance of distally mounted operativeelements supported by these catheter assemblies.

For example, as shown in FIG. 12, a typical ultrasonic imaging/ablationcatheter assembly 300 includes an elongate catheter body 302 withdistally mounted ablation electrodes 304 and a distally disposedrotatable ultrasonic transducer 306 to allow a physician to more easilyimage and ablate abnormal vasculature tissue.

The ablation electrodes 304 are electrically coupled to a proximallydisposed RF generator (not shown) via transmission lines 308, which arerouted through a first internal lumen 310 extruded within the catheterbody 302. Operation of the RF generator transmits radio frequencyelectrical energy through the transmission lines 308 to the ablationelectrodes 304, which in turn emit RF energy into the vasculature tissueadjacent the ablation electrodes 304.

The ultrasonic transducer 306 is mounted in a transducer housing 312disposed within the catheter body 302. The ultrasonic transducer 306 ismechanically and rotatably coupled to a proximally disposed drive unit(not shown) via a drive cable 314 rotatably disposed within a secondextruded internal lumen 316. The ultrasonic transducer 306 iselectrically coupled to a proximally disposed signal transceiver (notshown) via a transmission line (not shown) disposed within the drivecable 314. Operation of the drive unit rotates the drive cable 314, andthus the ultrasonic transducer 306, with respect to the catheter body302. Simultaneous operation of the transceiver alternately transmits andreceives electrical energy to and from the ultrasonic transducer 306 viathe drive cable disposed transmission line, thereby providing thephysician with 360° imaging of the vasculature tissue adjacent theultrasonic transducer 306.

The catheter assembly 300 is configured to allow the drive cable 314 anddistally mounted ultrasonic transducer 306 to be “back loaded” (i.e.,inserted or retracted) through the second interior lumen 316. The sizeof the ultrasonic transducer 306, and thus the integrity of the imagingdata obtained therefrom, is thus limited by the size of the secondinterior lumen 316. The size of the second interior lumen 316, however,could be increased by eliminating the first interior lumen 308.

Another concern with respect to intraluminal catheter assemblies is thecoupling of an electrical signal between a distal non-rotatableoperative element and a proximal rotatable operative element, such as,e.g., the ultrasonic transducer 306 and transceiver employed in thecatheter assembly 300 described above. Typically, to provide thisinductive coupling, an inductive coupler is connected in parallel withthe signal wires at the proximal end of the catheter. As such, thatportion of the signal wires distal to the inductive coupler rotate withthe transducer, and must therefore be installed within the entire lengthof the drive cable. Although a proximally disposed inductive coupleradequately provides inductive coupling between the transducer and thetransceiver, this arrangement has several disadvantages.

For example, a signal wire disposed drive cable aggravates a phenomenonsuffered by ultrasound imaging catheters called non-uniform rotationaldistortion (“NURD”). NURD is caused by frictional forces between therotating imaging core and the inner wall of the catheter, which aremagnified by the many twists and turns that a catheter must undergo sothat the transducer can be positioned in the desired imaging locationwithin the patient's body. These frictional forces cause the imagingcore to rotate about its axis in a non-uniform manner, thereby resultingin a distorted image.

NURD can be minimized by “optimizing” the construction of the drivecable, for example, by varying the drive cable's diameter, weight,material, etc. The characteristics of the drive cable, however, aredictated in part by the signal wires disposed therein, thereby limitingthis NURD-minimizing optimization. Further, the signal wires contributenon-uniformities to the drive cable that cannot be optimized.

A further disadvantage of a proximally disposed inductive coupler isthat the diameter of the drive cable must be increased to accommodatethe signal wires, thereby occupying space within the catheter that couldotherwise be used to support other functions such as, e.g., pull-wiresteerability, angioplasty balloon therapy, ablation therapy, or bloodflow (Doppler) measurements.

A further disadvantage of a proximally disposed inductive coupler isthat the remoteness of the coupler prevents usage thereof for transduceroptimization, i.e., transducer tuning and matching or prevention oftransducer low frequency mode emittance. Thus, additional measures mustbe employed to either optimize the transducer or to minimize theundesirable effects thereof.

For instance, at its normal frequency of operation, the transducerexhibits a net capacitive reactance. Thus, inductive reactance should beprovided to “cancel” this capacitive reactance, so as to efficientlycouple the transmit/receive signals to the transducer (e.g., to maximizesignal-to-noise ratios). A proximally disposed inductive coupler doesnot provide the needed inductance, however, since the inductanceproducing structure must be placed along the signal wires in closeproximity to the transducer. Instead, such a result can be accomplishedby placing an inductive coil in series with the signal wires, asdemonstrated in U.S. Pat. No. 4,899,757 issued to Pope, Jr. et al.

In addition to canceling the capacitive reactance produced by thetransducer, it is also desirable to match the input impedance of thetransducer with the characteristic impedance of the signal wires, so asto minimize signal reflection. In particular, a proximally disposedinductive coupler is by definition proximal to the signal wires and cantherefore not be used to perform such matching. An attempt can be madeto optimize the size and material of the transducer for matching of thesignal wires therewith. Such optimization is limited, however, and tothe extent any signal reflections are not eliminated, the signal powerwill accordingly be reduced.

Still further, an excited transducer naturally creates a low frequencymode of vibration that further produces multiples of higher frequencymodes (e.g., 4 MHz, 8 MHz, 12 MHz, etc.). These unwanted signals cannotbe eliminated through the use of a proximally disposed inductivecoupler, but must be filtered out at the proximal end of the catheter.The signals within the frequency band in which the imaging system is tobe operated cannot be filtered out, however, and must be dealt with asinterference.

Theoretically, a parallel inductor can be placed in close proximity tothe transducer to short out the low frequency mode, thereby eliminatingthe higher frequency modes. Such an arrangement, however, is complicatedand expensive, and thus inefficient for the mere purpose of eliminatingunwanted modes of transducer vibration.

Therefore, it would be desirable to increase the available space withina catheter body by eliminating or at least reducing the number ofinterior lumens that support transmission lines. It would be furtherdesirable to improve the mechanical and electrical performance of acatheter that employs a distal rotatable operative element and aproximal non-rotatable operative element.

SUMMARY OF THE INVENTION

The present invention overcomes the afore-described drawbacks ofconventional intraluminal catheter assemblies by providing improvedintraluminal catheter assemblies that employ a distally disposedinductive coupling assembly and/or at least one conductor embedded inthe exterior wall of an elongate catheter body to provide communicationbetween respective distal and proximal operative elements.

In a first preferred embodiment, a catheter assembly according to thepresent invention includes an elongate catheter body having a proximalend and a distal end with a drive cable disposed therein and rotatablerelative to the catheter body. A first electro-magnetic element isdisposed proximate the distal end of the catheter body and in electricalcommunication with a proximal operative element proximate the proximalend of the catheter body. A second electro-magnetic element is rotatablycoupled to the drive cable and in electrical communication with a distaloperative element rotatably coupled to the drive cable. The first andsecond electro-magnetic elements form an inductive coupler.

In accordance with a further aspect of the present invention, the firstelectro-magnetic element comprises a stator fixably disposed in thecatheter body, and the second electro-magnetic element comprises a rotormounted to a distal end of the drive cable, wherein the stator comprisesa generally hollow cylinder, and the rotor comprises a rod rotatablydisposed in the hollow cylinder. The stator and rotor are preferablymade of a ferrite material, with the stator having a first electricallyconductive coil disposed on the inner surface of the hollow cylinder,and wherein the rotor having a second electrically conductive coildisposed on the outer surface of the rod.

The stator and rotor having opposing surface areas, wherein therespective stator and rotor surface areas, along with the respectivediameter, size and number of turns of the first and second electricallyconductive coils, are selected such that the value of the inductivereactance of the inductive coupler is substantially equal to thecapacitive reactance of the operative element, which may be, e.g., anultrasonic transducer.

In accordance with a still further aspect of the present invention, thecatheter assembly includes a first conductor having a distal endelectrically coupled to the stator and a proximal end configured forelectrically coupling to a signal transceiver. Preferably, the firstconductor is disposed within the catheter body, with the ratio of turnsbetween the first and second electrically conductive coils beingselected such that the input impedance looking into the inductivecoupler from the transmission line substantially matches thecharacteristic impedance of the transmission line. The catheter assemblyincludes a second conductor having a proximal end electrically coupledto the rotor and a distal end electrically coupled to an ultrasonictransducer. The signal transceiver and ultrasonic transducer areconfigured to provide 360° imaging of body tissue, such as, e.g.,arterial tissue.

In a second preferred embodiment, a catheter assembly according to thepresent invention includes an elongate catheter body having a proximalend and a distal end with a drive cable disposed therein and rotatablerelative to the catheter body. First and second electro-magneticelements are disposed proximate the distal end of the catheter body andrespectively in electrical communication with first and second proximaloperative elements proximate the proximal end of the catheter body.Third and fourth electro-magnetic elements are rotatably coupled to thedrive cable and in electrical communication with first and second distaloperative elements rotatably coupled to the drive cable. The first andthird electro-magnetic elements form a first inductive coupler, and thesecond and fourth electro-magnetic elements form a second inductivecoupler.

In accordance with a further aspect of the present invention, the firstand second electro-magnetic elements respectively comprise first andsecond stators fixably disposed in the catheter body, and the third andfourth electro-magnetic elements comprise first and second rotorsmounted to a distal end of the drive cable, wherein the statorsrespectively comprise generally hollow cylinders, and the rotorsrespectively comprise rods rotatably disposed in the hollow cylinders,respectively.

In accordance with a still further aspect of the present invention, thecatheter assembly includes first and second conductors having distalends electrically coupled to the first and second stators, respectively,and proximal ends configured for electrically coupling to first andsecond signal transceivers, respectively. The catheter assembly includesthird and fourth conductors having proximal ends electrically coupled tothe first and second rotors, respectively, and distal ends electricallycoupled to first and second ultrasonic transducers, respectively. Thefirst signal transceiver and first ultrasonic transducer are configuredto provide 360° imaging of body tissue, such as, e.g., arterial tissue,and the second signal transceiver and second ultrasonic transducer areconfigured to provide Doppler measurements of the blood flow through avessel, such as, e.g., an artery.

In a third preferred embodiment, a catheter assembly according to thepresent invention includes an elongate telescoping catheter body havinga proximal end and a distal end with a drive cable disposed therein androtatable relative to the catheter body. A first electro-magneticelement is disposed proximate the distal end of the catheter body and inelectrical communication with a proximal operative element proximate theproximal end of the catheter body. A second electro-magnetic element isrotatably coupled to the drive cable and in electrical communicationwith a distal operative element rotatably coupled to the drive cable.The first and second electro-magnetic elements form an inductivecoupler. The telescoping catheter body is movably disposed in a maincatheter body to provide longitudinal displacement of the distaloperative element relative to the main catheter body. The particularaspects of the third preferred embodiment are similar to those of thefirst preferred embodiment with the exception that the controlledlongitudinal displacement of the telescoping catheter body relative tothe main catheter body allows for longitudinally spaced 360° imageslices.

In a fourth preferred embodiment, a catheter assembly according to thepresent invention includes an elongate catheter body with a first distaloperative element disposed thereon. The first distal operative elementis electrically coupled to a first proximal operative element via atransmission line embedded in the wall of the catheter body. Thecatheter assembly includes a drive cable and a second distal operativeelement rotatably coupled to the drive cable. The second distaloperative element is electrically coupled to a second proximal operativeelement via a transmission line within the drive cable.

In accordance with a further aspect of the invention, the first distaloperative element comprises a first ultrasonic transducer mounted to thedistal end of the catheter body, such that the face of the ultrasonictransducer is perpendicular to the axis of the catheter body. The seconddistal operative element comprises a second ultrasonic transducermounted to the distal end of the drive cable. The first and secondproximal elements respectively comprise signal transceivers. The firstsignal transceiver and first ultrasonic transducer are configured toprovide Doppler measurements of the blood flow through a vessel, suchas, e.g., an artery, and the second signal transceiver and secondultrasonic transducer are configured to provide 360° imaging of bodytissue, such as, e.g., arterial tissue. The catheter wall can be used asa portion of the transmission line.

In a fifth preferred embodiment, a catheter assembly according to thepresent invention includes an elongate catheter body with first andsecond distal operative elements disposed thereon. The first and seconddistal operative elements are electrically coupled to a first proximaloperative element via respective first and second transmission linesembedded in the wall of the catheter body. The catheter assemblyincludes a drive cable and a third distal operative element rotatablycoupled to the drive cable. The third distal operative element iselectrically coupled to a second proximal operative element via a thirdtransmission line within the drive cable.

In accordance with a further aspect of the invention, the first andsecond distal operative elements comprise respective first and secondelectrodes, such as, e.g., ablation electrodes, mounted to the distalend of the catheter body. The first proximal element comprises an RFgenerator. The third distal operative element comprises an ultrasonictransducer mounted to the distal end of the drive cable. The secondproximal element comprises a signal transceiver. The first and secondablation elements and the RF generator are configured to provideablation therapy to adjacent body tissue, such as, e.g., arterialtissue, and the ultrasonic transducer and signal transceiver areconfigured to provide 360° imaging of body tissue, such as, e.g.,arterial tissue.

In a sixth preferred embodiment, a catheter assembly according to thepresent invention includes an elongate catheter body with a plurality ofdistal operative elements disposed thereon. The plurality of distaloperative elements are respectively electrically coupled to at least oneproximal operative element via a plurality of transmission linesembedded in the wall of the catheter body.

In accordance with a further aspect of the invention, the plurality ofdistal operative elements comprise respective transducer elements, whichare circumferentially arranged around the catheter body to form a phasedarray. The proximal element comprises a transceiver, which is configuredto provide phased electrical signals to the plurality of transducerelements.

Other and further objects, features, aspects, and advantages of thepresent invention will become better understood with the followingdetailed description of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate both the design and utility of preferredembodiments of the present invention, in which:

FIGS. 1A and 1B are cut-away, partial side views of a first preferredcatheter assembly employing a distal inductive coupler;

FIG. 2 is a cut-away, partial side view of the catheter assembly ofFIGS. 1A and 1B;

FIGS. 3A and 3B are cut-away, partial side views of a second preferredcatheter assembly employing a distal inductive coupler;

FIG. 4 is a cut-away, partial side view of the catheter assembly ofFIGS. 3A and 3B;

FIGS. 5A and 5B are cut-away, partial side views of a third preferredcatheter assembly employing a distal inductive coupler;

FIG. 6 is a cut-away, partial side view of the catheter assembly ofFIGS. 5A and 5B;

FIGS. 7A and 7B are cut-away, partial side views of a fourth preferredcatheter assembly employing an embedded transmission line;

FIG. 8 is a cut-away, partial side view of the catheter assembly ofFIGS. 7A and 7B;

FIGS. 9A and 9B are cut-away, partial side views of a fifth preferredcatheter assembly employing two embedded transmission lines;

FIG. 10 is a cut-away, partial side view of the catheter assembly ofFIGS. 9A and 9B;

FIG. 11 is a cross-sectional view of the catheter assembly of FIGS. 9Aand 9B employing four embedded transmission lines;

FIG. 12 is a cut-away, partial side view of a prior art catheterassembly employing an interior lumen disposed transmission line;

FIG. 13 is a cut-away, cross-sectional view of the guide sheath andtransmission line of the catheter assembly of FIGS. 7A and 7B; and

FIGS. 14A and 14B are cut-away, partial side views of a fifth preferredcatheter assembly employing two embedded transmission lines.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1A, 1B and 2, a first exemplary catheter assembly 10according to the present invention is provided for ultrasonic imaging ofa patient's internal body tissue, e.g., the wall of an artery. Thecatheter assembly 10 generally includes an elongate catheter body 12, adistal inductive coupler 14, a drive cable 18, a rotatable distaloperative element 16, and a non-rotatable proximal operative element 17.The drive cable 18 is disposed through substantially the entire catheterbody 12, both of which are suitably mounted at the respective proximalends thereof to a drive unit 19 proximal to the catheter assembly 10.

The inductive coupler 14 is disposed in the distal end of the catheterbody 12 and generally includes a stator 20 and a rotor 22. The stator 20is fixably mounted in the distal end of the catheter body 12. Inparticular, the stator 20 is supported by the inner surface of thecatheter body 12, such as by way of heat shrinking the catheter body 12over the stator 20. It can be appreciated, however, that other methodsof fixing the stator 20 within the catheter body 12 can be accomplishedby, e.g., embedding the stator 20 at least partially within the wall ofthe catheter body 12.

The rotor 22 is rotatably mounted inside the stator 20. In particular,the stator 20 includes a generally hollow cylinder 21 having a generallyuniform inner diameter. The stator 20 includes an annular flange 38integrally formed on the inner surface of the hollow cylinder 21 at theproximal end thereof. The stator 20 includes respective first and secondapertures 34 and 36 through which the rotor 22 extends.

In particular, the distal end of the hollow cylinder 21 defines thefirst aperture 34, which has a diameter equal to the inner diameter ofthe hollow cylinder 21. The annular flange 38 defines the secondaperture 36, which has a diameter smaller than that of the firstaperture 34. The rotor 22 comprises a cylindrical rod 40 and a bearingdisk 42 formed on and preferably integral with the distal end of thecylindrical rod 40. The diameters of the rod 40 and bearing disk 42 aresubstantially equal to the diameters of first aperture 34 and the secondaperture 36, respectively, such that disposal of the rotor 22 in thestator 20 creates a first bearing surface 44 and a second bearingsurface 46 therebetween.

In this manner, the respective first and second bearing surfaces 44 and46 prevent lateral movement of the rotor 22 relative to the stator 20.The significance of the positional relationship of the rotor 22 and thestator 20 is the close proximity therebetween, such that the inductiveefficiency between the stator 20 and the rotor 22 is maximized.

That is, an alternating electrical current applied to either the stator20 or the rotor 22 creates a corresponding alternating electricalcurrent on the other when the rotor 22 rotates relative to the stator20. Thus, the rotor 22 and stator 20 can also, e.g., comprise rotatableand non-rotatable disks, respectively, that face one another.

The rotor 22 includes a thrust disk 48 and a thrust washer 50. Thethrust disk 48 is formed on and preferably integral with the distal endof the rod 40. The thrust washer 50 is disposed about and fixed to theproximal end of the rod 40. The thrust disk 48 and thrust washer 50cooperate to form a first thrust surface 52 and a second thrust surface54.

More particularly, the thrust disk 48 has a diameter greater than thatof the first aperture 34 and is distally adjacent to the stator 20, suchthat the proximal surface of the thrust disk 48 is in contact with thedistal surface of the stator 20. The thrust washer 50 has a diametergreater than that of the second aperture 36 and is proximally adjacentto the stator 20, such that the distal surface of the thrust washer 50is in contact with the proximal surface of the stator 20. In thismanner, the respective first and second thrust surfaces 52 and 54prevent longitudinal movement of the rotor 22 relative to the stator 20.

The distal operative element 16 comprises an ultrasonic transducerelement 28 fixably mounted to a conductive housing 30, such that theface of the transducer element 28 is substantially parallel to the axisof the elongate catheter body 12. In preferred embodiments, there is aslight angle between the face of the transducer element 28 and the axisof the catheter assembly 10, thereby resulting in a “conical sweep”during imaging.

The proximal element 17 comprises a transceiver for alternatelytransmitting and receiving electrical signals to and from the transducerelement 28 to obtain data for imaging the walls of the vessel in whichthe catheter assembly 10 is disposed. It can be appreciated, however,that the distal operative element 16 and the proximal operative element17 are not limited to a transducer element 28 and a transceiver,respectively, but can, without straying from the principles taught bythis invention, respectively comprise any rotatable and non-rotatabledevice that are in electrical communication with one another.

A conductive transducer backing material 32 made of a suitable materialis potted in the housing 30 and beneath the transducer element 28, suchthat substantially all of the ultrasonic energy emitted by thetransducer element 28 into the transducer backing material 32 isattenuated therein.

Conversely, a transducer matching material made of a suitable materialis bonded to the face of the transducer element 28 as a transducermatching layer 33 opposite the transducer backing material 32. Thepurpose of the matching layer, or multiple matching layers, 33 is toimprove transducer efficiency by maximizing the propagation of energythrough the matching layer(s) and enhance the signal bandwidth. Thetransceiver 17 is mounted within the drive unit 19. The transceiver 17can, however, be mounted to any stationary platform that is proximal tothe inductive coupler 14 without straying from the principles taught bythis invention

The housing 30, the rotor 22, and the drive cable 18 are mechanicallyand rotatably coupled to the drive unit 19, so that they rotate as anintegral unit relative to the stator 20 when the drive unit 19 isoperated. In particular, the proximal end of the drive cable 18 issuitably mounted to the drive unit 19 using means known in the art. Thedrive cable 18 is preferably designed such that it possesses a hightorsional stiffness and a low bending stiffness.

For example, the drive cable 18 can be made of two counterwound layersof multifilar coils that are fabricated using techniques disclosed inCrowley et al., U.S. Pat. No. 4,951,677, and fully incorporated hereinby reference. The proximal end of the rod 40 is suitably mounted to theinside of the drive cable 18 using known means such as welding. Therotor 22 includes a housing mounting disk 56 formed on and preferablyintegral with the proximal end of the rod 40. The housing mounting disk56 is distal to the bearing disk 48, and is suitably mounted to theinside of the housing 30 using known means such as welding.

The transceiver 17 is electrically coupled to the transducer element 28through the inductive coupler 14 and respective first and secondtransmission lines 24 and 26. In particular, the transceiver 17 iselectrically coupled to the stator 20 via the first transmission line24. The first transmission line 24 is preferably twisted pair, but canbe any electrical conductor used in the manufacture of catheters, suchas, e.g., coaxial cable. The first transmission line 24 is fixedrelative to the stator 20 and is preferably disposed within the catheterbody 12 using known extrusion methods, such as that disclosed inWoinowski, U.S. Pat. No. 4,277,432, and fully incorporated herein byreference. However, the first transmission line 24 can alternatively bedisposed within a catheter lumen using means known in the art.

The transducer element 28 is electrically coupled to the rotor 22 of theinductive coupler 14 via the second transmission line 26. Again, thesecond transmission line 26 is preferably made of twisted pair, but canalso be made of coaxial cable. The second transmission line 26 issuitably bonded to the rotor 22 and housing 30, such that the secondtransmission line 26 integrally rotates with the housing 30, rotor 22,and drive cable 18.

As mentioned above, the stator 20 and the rotor 22 are inductivelycoupled. In particular, the inductive coupler 14 includes an annularspace 57 formed between the inner surface of the cylinder 21 and theouter surface of the rod 40. The stator 20 includes a first electricallyconductive coil 58 disposed in the annular space 57 and suitably bondedto the inner surface of the cylinder 21. The rotor 22 includes a secondelectrically conductive coil 55 disposed in the annular space 57 andsuitably bonded to the outer surface of the rod 40. The annular space 57allows a close positional relationship between the respective first andsecond coils 58 and 55 without any contact therebetween.

The first transmission line 24 is connected to each end of the coil 58,and the second transmission line 26 is connected to each end of thesecond coil 55. In this manner, the transceiver 17 and the transducerelement 28 are electrically connected in parallel to the stator 20 andthe rotor 22, respectively.

To maximize the inductive efficiency of the inductive coupler 14, thestator 20 and the rotor 22 are preferably made of a magnetic materialsuch as ferrite, and the respective first and second coils 58 and 55 arepreferably made of copper. The particular characteristic impedance ofthe inductive coupler 14 are preferably chosen so as to tune the signalcarrying capability of the first transmission line 24.

That is, the wire diameter, size, and number of turns of the respectivefirst and second coils 58 and 55 and the surface area of the stator 20and the rotor 22 are chosen, such that the inductive coupler 14 exhibitsan inductive reactance which is substantially equivalent to the netcapacitive reactance of the transducer element 28 at the operatingfrequency thereof. Also, to prevent signal reflections between thesecond transmission line 26 and the inductive coupler 14, the ratio ofturns between the respective first and second coils 58 and 55 preferablyshould be chosen, such that the input impedance looking into theinductive coupler 14 matches the characteristic impedance of the firsttransmission line 24.

In use, the catheter assembly 10 is intravascularly inserted into apatient. For example, if the catheter assembly 10 is to be used so as toimage a patient's coronary arteries, then it may conveniently beinserted percutaneously into the patient's femoral artery. The catheterassembly 10 is then maneuvered by the physician until a desired regionof the patient's coronary arteries is adjacent the transducer element28.

With the catheter assembly 10 properly positioned, ultrasonic imaging ofthe adjacent arterial tissue may be accomplished conventionally bytransmitting electrical pulses to and receiving electrical pulses fromthe rotating transducer element 28.

In particular, the drive unit 19 is operated to rotate the transducerelement 28 at a high rotational speed. In particular, the drive unit 19provides rotational energy to the drive cable 18, which in turn providesrotational energy to the transducer element 28 via the rotor 22 of theinductive coupler 14. Prevention of any lateral and longitudinalmovement of the rotor 22 with respect to the stator 20 via the bearingsurfaces 44 and 46 and the thrust surfaces 52 and 54, respectively,allows a uniform inductive relationship between the stator 20 and therotor 22.

The transceiver 17 transmits an electrical pulse to the stator 22 viathe first transmission line 24, thereby charging the first coil 58. Thecharge on coil 58 is inductively coupled to the coil 55. The inductivecoupling is maximized by the close positional relationship between thestator 20 and the rotor 22 at the respective first and second bearingsurfaces 44 and 46. The inductive charge on the second coil 55 is thentransmitted to the transducer element 28 via the second transmissionline 26.

The electrically excited transducer element 28 emits ultrasonic energy,which reflects off of the arterial wall of the patient and back into thetransducer element 28. This reflected ultrasonic energy produces areturn electrical signal in the transducer element 28, which istransmitted back to the rotor 22 via the second transmission line 26,thereby charging the second coil 55. The charge on the coil 55 isinductively coupled to the coil 58. The inductive charge on the firstcoil 58 is then transmitted back to the transceiver 17 via the firsttransmission line 24. This return electrical signal is further processedas imaging data. The transceiver 17 alternately transmits electricalpulses to and receives return electrical signals from the transducerelement 28 to obtain further imaging data.

Since the inductive coupler 14 is located closely adjacent thetransducer element 28, an effectively increased signal to noise ratioresults with the benefit being that higher quality imaging signals aretransmitted into the transceiver 17. That is, since the inductivereactance of the inductive coupler 14 is equivalent to the netcapacitive reactance of the transducer element 28, the reactive power ofthe return electrical pulse is minimized.

Further, since the inductive coupler 14 is used to match the impedanceof the transducer element 28 to the characteristic impedance of thefirst transmission line 24, signal reflections are minimized. Lastly,since the inductive coupler 14 is electrically connected in parallel tothe transducer element 28, the inductive coupler 14 shorts out any lowfrequency modes of vibration produced by the transducer element 28, thuspreventing non-filterable higher frequency modes from being furtherproduced. As such, the signal to noise ratio of the return electricalsignal is increased, thus resulting in higher quality imaging.

Referring to FIGS. 3A, 3B and 4, a second exemplary catheter assembly 60is provided for measuring the velocity of the blood within a patient'svessel, while also providing ultrasonic imaging of the vessel wall. Thecatheter assembly 60 generally includes an elongate catheter body 62,respective first and second distal inductive couplers 64 and 65, a drivecable 66, respective first and second rotatable distal operativeelements 68 and 70, and respective first and second non-rotatableproximal operative elements 72 and 74.

The drive cable 66 is disposed through substantially the entire catheterbody 62, both of which are mounted at the respective proximal endsthereof to a drive unit 76 proximal to the catheter assembly 60. Therespective first and second inductive couplers 64 and 65 are disposed inthe distal end of the catheter body 62 and generally include a firststator 78 and first rotor 82, and a second stator 80 and second rotor83, respectively. The respective first and second inductive couplers 64and 65 are in a coaxial relationship with each other.

In particular, the respective first and second stators 78 and 80 aresupported by the inner surface of the catheter body 62, such as by wayof heat shrinking the catheter body 62 thereover. It can be appreciated,however, that other methods of fixing the respective first and secondstators 78 and 80 within the catheter body 62 can be accomplished by,e.g., embedding the respective first and second stators 78 and 80 atleast partially within the wall of the catheter body 62.

The structures of the respective first and second inductive couplers 64and 65 are similar to the structure described above with respect to theinductive coupler 14 of the catheter assembly 10, with the exceptionthat the first rotor 82 lacks a thrust washer and the second rotor 83lacks a housing mounting disk and a thrust disk. The first stator 78 andthe first rotor 82 form first and second bearing surfaces 85 and 87 anda first annular space 93 therebetween, and the second stator 80 and thesecond rotor 83 form third and fourth bearing surfaces 89 and 91 and asecond annular space 95 therebetween.

The catheter assembly 60 includes an isolation disk 84 disposed betweenthe respective first and second inductive couplers 64 and 65. Theisolation disk 84 is made of an electrical insulative material toprevent electrical conduction between the respective first and secondinductive couplers 64 and 65.

In particular, the proximal end of the first stator 78 and the distalend of the second stator 80 respectively abut the distal and proximalfaces of the isolation disk 84. The proximal end of the first rotor 82and the distal end of the second rotor 83 are fixably mounted to thedistal and proximal faces of the isolation disk 84, respectively.Preferably, the faces of the isolation disk 84 have recesses formedtherein to receive the respective ends of the rotors 82 and 83.

The second rotor 83 includes a thrust washer 86 disposed about and fixedto the proximal end of the rod rotor 83. A thrust disk 79 formed at thedistal end of the first rotor 82, the thrust washer 86, and theisolation disk 84 cooperate to form respective first, second, third, andfourth thrust surfaces 97, 99, 101 and 103 in much the same manner asthat described above with reference to the inductive coupler 22 of thecatheter assembly 10.

In this manner, the inductive efficiency of the respective first andsecond inductive couplers 64 and 65 is increased. In particular, thebearing surfaces 85, 87, 89, and 91 and thrust surfaces 97, 99, 101, and103 provide a close positional relationship and prevent lateral andlongitudinal movement between the stators 78 and 80 and rotors 82 and83, respectively.

The first distal operative element 68 comprises a first ultrasonictransducer 88 fixably mounted to a conductive housing 81, such that theface of the first ultrasonic transducer element 88 is substantiallyparallel to the axis of the elongate catheter body 62.

In preferred embodiments, there is a slight angle between the face ofthe first ultrasonic transducer element 88 and the axis of the catheterassembly 60, thereby resulting in a “conical sweep” during imaging. Thefirst proximal element 72 comprises a first transceiver for alternatelytransmitting and receiving electrical signals to and from the firsttransducer element 88 to obtain data for imaging the walls of the vesselin which the catheter assembly 60 is disposed.

The second distal operative element 70 comprises a second ultrasonictransducer element 90 fixably mounted to the distal end of theconductive housing 81, such that the face of the second transducerelement 90 is substantially perpendicular to the axis of the elongatecatheter body 62.

The second proximal element 74 comprises a second transceiver foralternately transmitting and receiving electrical signals to and fromthe second transducer element 90 to obtain data for Doppler measurementsof the blood flow within the vessel in which the catheter assembly 60 isdisposed. It can be appreciated, however, that the distal operativeelements 68 and 70 and proximal operative elements 72 and 74 are notrespectively limited to the transducer elements 88 and 90 and thetransceivers, but can, without straying from the principles taught bythis invention, respectively comprise any rotatable and non-rotatabledevices that are in electrical communication with one another.

A conductive transducer backing material 92 made of a suitable materialis potted in the housing 81, such that substantially all of theultrasonic energy emitted by the transducer elements 88 and 90 into thetransducer backing material 92 is attenuated therein.

Conversely, transducer matching material made of a suitable material isformed onto the faces of the respective transducer elements 88 and 90 asrespective transducer matching layers 105 and 107 opposite thetransducer backing material 92. The purpose of the matching layer 105and 107, or multiple matching layers, is to improve transducerefficiency by maximizing the propagation of energy through the matchinglayer(s), and enhance the signal bandwidth. The respective transceivers72 and 74 are mounted within the drive unit 76, but can, however, bemounted to any stationary platform that is proximal to the inductivecoupler 64 without straying from the principals taught by thisinvention.

The rotors 82 and 83 are mechanically and rotatably mounted to thehousing 81 and the drive cable 66, respectively, in much the same manneras that described above with reference to the rotor 22, housing 30, anddrive cable 18. Thus, the housing 81, the respective first and secondrotors 82 and 83, and the drive cable 66 rotate as a single unit.

The first transceiver 72 is electrically coupled to the first transducerelement 88 through the first inductive coupler 64 and respective firstand second transmission lines 94 and 96, and the second transceiver 74is electrically coupled to the second transducer element 90 through thesecond inductive coupler 65 and respective third and fourth transmissionlines 98 and 100 in much the same manner as described above with respectto the transceiver 17 and the transducer element 28 of the catheterassembly 10.

In particular, the transceivers 72 and 74 are respectively electricallycoupled to the stators 78 and 80, via respective first and thirdtransmission lines 94 and 98. The transmission lines 94 and 98 arepreferably twisted pair, but can be any electrical conductor used in themanufacture of catheters, such as, e.g., coaxial cable. The first andthird transmission lines 94 and 98 are respectively fixed relative tothe stators 78 and 80, and are preferably disposed within the catheterbody 62 using known extrusion methods. The transmission lines 94 and 98,however, can also be disposed within a catheter lumen (not shown) usingmeans known in the art.

The transducer elements 88 and 90 are respectively electrically coupledto the rotors 82 and 83, via respective second and fourth transmissionlines 96 and 100. Again, the transmission lines 96 and 100 arepreferably made of twisted pair, but can also be made of coaxial cable.The second transmission line 96 is suitably bonded to the first rotor 82and the housing 81, and the fourth transmission line 100 is suitablybonded to the second rotor 83 and the housing 81, such that thetransmission lines 96 and 100 integrally rotate with the housing 81, therotors 82 and 83, and the drive cable 66.

As mentioned above, the stators 78 and 80 are inductively coupled to therotors 82 and 83, respectively. In particular, the first stator 78 andthe second stator 80 respectively include a first electricallyconductive coil 102 and a third electrically conductive coil 106suitably bonded to the inner surfaces thereof, and the first rotor 82and the second rotor 83 include a second electrically conductive coil104 and a fourth electrically conductive coil 108 suitably bonded to theouter surfaces thereof.

The first annular space 93 formed between the first stator 78 and thefirst rotor 82, and the second annular space 95 formed between thesecond stator 80 and the second rotor 83 allow a close positionalrelationship between the respective first and second coils 102 and 104and between the respective third and fourth coils 104 and 108, withoutany contact therebetween. The respective first, second, third, andfourth transmission lines 94, 96, 98, and 100 are connected to the endsof the respective first, second, third, and fourth coils 102, 104, 106,and 108, respectively, as shown.

In this manner, the respective first and second transceivers areelectrically connected in parallel to the respective first and secondstators 78 and 80, respectively, and the respective first and secondtransducer elements 88 and 90 are electrically connected in parallel tothe respective first and second rotors 82 and 83, respectively.

As with the inductive coupler 14 of the catheter assembly 10, thevarious parameters of the respective first and second inductive couplers64 and 65 can be chosen to maximize the efficiency of the catheterassembly 60.

In use, the catheter assembly 60 is intravascularly inserted into apatient in much the same manner as that described above with referenceto the catheter assembly 10. With the catheter assembly 60 properlypositioned, ultrasonic imaging of the adjacent arterial tissue may beaccomplished conventionally with the first transducer element 88 in muchthe same manner as that described above with respect to the catheterassembly 10.

In addition, catheter assembly 60 can be employed to provide Dopplerdata on the blood velocity within the blood vessel by transmittingelectrical pulses to and receiving electrical signals from the secondtransducer element 90.

In particular, the second transceiver transmits an electrical signal tothe second stator 80 via the third transmission line 98, therebycharging the third coil 106. The charge on the third coil 106 isinductively coupled to the fourth coil 108. This inductive coupling ismaximized by the close positional relationship between the second stator80 and the second rotor 83 at the respective third and fourth bearingsurfaces 89 and 91. The inductive charge on the fourth coil 108 is thentransmitted to the second transducer element 90 via the fourthtransmission line 100.

The electrically excited second transducer element 90 emits ultrasonicenergy, which reflects off of the blood flowing in the vessel and backinto the second transducer element 90. This reflected ultrasonic energyproduces a return electrical signal in the second transducer element 90,which is transmitted back to the second rotor 83 via the fourthtransmission line 100, thereby charging the fourth coil 108. The chargeon the fourth coil 108 is inductively coupled to the third coil 106.

The inductive charge on the third coil 106 is then transmitted back tothe second transceiver via the third transmission line 98. This returnelectrical pulse is further processed as Doppler data. The secondtransceiver alternately transmits electrical pulses to and receivesreturn electrical signals from the second transducer element 90 toobtain further Doppler data.

The benefits and advantages obtained by disposing the respective firstand second inductive couplers 64 and 65 in the distal end of catheterassembly 60 adjacent to the respective first and second transducerelements 88 and 90 are the same as described above with respect tocatheter assembly 10.

Referring to FIGS. 5A, 5B, and 6, a third exemplary catheter assembly120 generally includes a main elongate catheter body 122, a telescopingelongate catheter body 124, a distal inductive coupler 126, a drivecable 128, a rotatable distal operative element 130, and a non-rotatableproximal operative element 132. The telescoping catheter body 124 ismovably disposed in the main catheter body 122. The drive cable 128 isdisposed through substantially the entire telescoping catheter body 124.The drive cable 128, the main catheter body 122, and the telescopingcatheter body 124 are mounted at the respective proximal ends thereof toa drive unit 134 proximal to the catheter assembly 120. The drive unit134 can be any drive unit that is suitable for use with a telescopingcatheter, of which many are known in the art.

The inductive coupler 126 is disposed in the distal end of thetelescoping catheter body 124 and generally includes a stator 136 and arotor 138. The distal operative element 130 is disposed in the maincatheter body 122 distal to the telescoping catheter body 124. Theoperative element 130 can, however, be partially or fully disposed inthe distal end of the telescoping catheter body 124.

In particular, the structure and positional relationship between thestator 136 and the rotor 138 of the inductive coupler 126 is similar tothat described above with respect to the stator 20 and the rotor 22 ofthe inductive coupler 14 of catheter assembly 10. The distal operativeelement 130 comprises an ultrasonic transducer 140 with transducermatching and backing layers (not shown) fixably mounted to a conductivehousing 142 in much the same manner as described above with respect tothe transducer 28 and the housing 30 of the catheter assembly 10.

The proximal element 132 comprises a transceiver for alternatelytransmitting and receiving electrical signals to and from the transducer140 to obtain data for imaging the walls of the vessel in which thecatheter assembly 120 is disposed. It can be appreciated, however, thatthe distal operative element 130 and the proximal operative element 132are not limited to the transducer 140 and the transceiver, respectively,but can, without straying from the principles taught by this invention,respectively comprise any rotatable and non-rotatable device that are inelectrical communication with one another.

The transceiver 132 is mounted within the drive unit 134. Thetransceiver 132 can, however, be mounted to any stationary platform thatis proximal to the inductive coupler 126 without straying from theprinciples taught by this invention.

The housing 142, the rotor 138, and the drive cable 128 are mechanicallyand rotatably coupled to the drive unit 134 in much the same manner asdescribed above with respect to the housing 30, the rotor 22, the drivecable 18, and the drive unit 19 of catheter assembly 10. Likewise, thetransceiver 132 is electrically coupled to the transducer 140 throughthe inductive coupler 126 and respective transmission lines 144 and 146in much the same manner as described above with respect to thetransceiver 17 and the transducer element 28 of catheter assembly 10,with the exception that the first transmission line 144 is disposed inthe telescoping catheter body 124.

In use, the catheter assembly 120 is intravascularly inserted into apatient in much the same manner as that described above with referenceto catheter assembly 10. With the catheter assembly 120 properlypositioned, ultrasonic imaging of the adjacent arterial tissue may beaccomplished conventionally with the transducer element 140 in much thesame manner as that described above with respect to catheter assembly10.

In addition, by manually operating the drive unit 134, the telescopingcatheter body 124 can be moved longitudinally relative to the maincatheter body 122 to place the transducer 140 adjacent to variousdesired imaging locations within the patient's vessel. Further, byautomatically operating the drive unit 134, the telescoping catheterbody 124 can be moved longitudinally relative to the main catheter body122 in a controlled and uniform manner to data samples representinglongitudinally spaced-apart 360 “slices” of the patient's interiorvessel walls, which can then be reconstructed using known algorithms anddisplayed in two-dimensional or three-dimensional formats on a consolemonitor (not shown).

Referring to FIGS. 7A, 7B, and 8, a fourth exemplary catheter assembly150 is provided for measuring the velocity of the blood within apatient's vessel, while also providing ultrasonic imaging of the vesselwall. The catheter assembly 150 generally includes an elongate catheterbody 152, a drive cable 154, a rotatable distal operative element 156, anon-rotatable distal operative element 158 and respective first andsecond non-rotatable proximal operative elements 160 and 162. The drivecable 154 is disposed through substantially the entire catheter body152, both of which are mounted at the respective proximal ends thereofto a drive unit 164 proximal to the catheter assembly 150. Although therespective proximal operative elements 160 and 162 are shown as beingdisposed in the drive unit 164, the respective proximal operativeelements 160 and 162 can be disposed external to the drive unit 164without straying from the principles taught by this invention.

The non-rotatable distal operative element 158 comprises a firstultrasonic transducer element 166 (forward-looking transducer) forperforming diagnostic functions such as Doppler measuring bloodvelocity. The first transducer element 166 is embedded in the distal tipof the catheter body 152, such that the face of the transducer element166 is substantially perpendicular to the axis of the catheter body 152.A conductive transducer backing material 168 is potted beneath the firsttransducer element 166, and a transducer matching material 170 is bondedto the face of the transducer element 166 as a transducer matching layer170 opposite the transducer backing material 168.

Alternatively, the non-rotatable distal operative element 158 comprisesone or more ultrasonic transducer elements embedded in the catheter body152, such that the face of the transducer element(s) are substantiallyparallel to the axis of the guide sheath. In this manner, the ultrasonictransducer elements can facilitate therapeutic functions, such as, e.g.,micro-bubble encapsulated drug delivery. In this case, a concentratedultrasound signal is provided to a diseased site in conjunction with thedelivery of the micro-bubble encapsulated drugs, which are burst by theultrasonic energy and released at the diseased site.

The first non-rotatable proximal element 160 comprises a firsttransceiver for alternately transmitting and receiving electricalsignals to and from the first transducer element 166 to obtain data forDoppler measurements of the blood flow within the vessel in which thecatheter assembly 150 is disposed. It can be appreciated, however, thatthe non-rotatable distal element 158 and the first non-rotatableproximal element 160 are not limited to a transducer element andtransceiver, respectively, but can, without straying from the principlestaught by this invention, respectively comprises any non-rotatabledevices that are in electrical communications with one another.

The first transceiver 160 is electrically coupled to the firsttransducer element 166 through a first transmission line 172. The firsttransmission line 172 is preferably twisted pair, but can be anyelectrical conductor used in the manufacture of catheters, such as,e.g., coaxial cable. The first transmission line 172 is embedded withinthe wall of the catheter body 152 using an extrusion process. To providea uniform impedance, it is essential during the extrusion process tominimize the presence of irregularities such as bubbles, and to keepconstant the spacing of the transmission line within the catheter body152. This results in a transmission line that is uniformly embeddedwithin the catheter body 152 and having a uniform impedance through thelength of the catheter body 152 for optimal signal transfer.

Preferably, the catheter body 152 forms a portion of the firsttransmission line 172. For example, as depicted in FIG. 13, the firsttransmission line 172 can be formed of two wires 173 with the catheterbody 152 acting as the dielectric material between the wires 173. Byusing the equation, z=[120/sqrt(er)]*[In(2*s/d)], (where z=impedance,s=separation between the wire in inches, d=diameter of wire in inches,and er=effective relative dielectric constant of medium between thewires), the proper characteristic impedance of the transmission line 172can be obtained. For instance, if the diameter (d) of the wires 173 is0.010 inches, the separation (s) between the wires is 0.02 inches, andthe effective relative dielectric constant (er) of the catheter body 152is 2.7, then the impedance (z) of the transmission line 172 will be 100ohms. Preferably, the wires 173 are insulated and twisted duringextrusion, resulting in a uniform spacing of the twisted pair. It shouldbe noted that twisting the wires is not required to achieve a uniformimpedance, but is used to facilitate a uniform spacing of the wires.

The rotatable distal operative element 156 comprises a second ultrasonictransducer element 174 for performing ultrasonic imaging of the vesselwall. The second transducer element 174 is fixably mounted to a housing176, such that the face of the second transducer element 174 issubstantially parallel to the axis of the catheter body 152. Inpreferred embodiments, there is a slight angle between the face of thesecond transducer element 174 and the axis of the catheter assembly 150,thereby resulting in a “conical sweep” during imaging. A conductivetransducer backing material 178 made of a suitable material is potted inthe housing 176 and beneath the second transducer element 174, and atransducer matching material made of a suitable material is bonded tothe face of the second transducer element 174 as a transducer matchinglayer 180 opposite the transducer backing material 178.

The second non-rotatable proximal element 162 comprises a secondtransceiver for alternately transmitting and receiving electricalsignals to and from the second transducer element 174 to obtain data forimaging the walls of the vessel in which the catheter assembly 150 isdisposed. It can be appreciated, however, that the rotatable distaloperative element 156 and the second non-rotatable proximal operativeelement 162 are not limited to a transducer element and a transceiver,respectively, but can, without straying from the principles taught bythis invention, respectively comprise any rotatable and non-rotatabledevice that are in electrical communication with each other.

The housing 176 and the drive cable 154 are mechanically and rotatablecoupled to the drive unit 164, so that the drive unit 164 can rotate thedrive cable 154 and the housing 176 as an integral unit. In particular,the proximal end of the drive cable 154 is suitably mounted to the driveunit 164 using means known in the art. The drive cable 154 is preferablydesigned in much the same manner as the drive cable 18 described withrespect to the catheter assembly 10.

The second transceiver 162 is electrically coupled to the secondtransducer element 174 through a second transmission line 182. Thesecond transmission line 182 is preferably coaxial cable, but can be anyelectrical conductor used in the manufacture of catheters, such as,e.g., twisted pair. The second transmission line 182 is disposed in thedrive cable 154 using means known in the art.

The catheter assembly 150 performs ultrasonic imaging and/or Dopplermeasurements in much the same manner as that described with respect tothe catheter assembly 60, with the exception that the first transmissionline 172 eclipses the second transducer element 174, thereby slightlyreducing the imaging capability of the catheter assembly 150.

Referring to FIGS. 9A, 9B, 10 and 11, a fifth exemplary catheterassembly 190 is provided for performing therapeutic applications such asablation therapy, while also providing ultrasonic imaging of the vesselwall. The catheter assembly 190 generally includes an elongate catheterbody 192, a drive cable 194, a rotatable distal operative element 196,respective first and second non-rotatable distal operative elements 198and 200 and respective first and second non-rotatable proximal operativeelements 202 and 204. The drive cable 194 is disposed throughsubstantially the entire catheter body 192, both of which are mounted atthe respective proximal ends thereof to a drive unit 206 proximal to thecatheter assembly 190. Although the respective proximal operativeelements 202 and 204 are shown as being disposed in the drive unit 206,the respective proximal operative elements 202 and 204 can be disposedexternal to the drive unit 206 without straying from the principlestaught by this invention.

In particular, the first and second non-rotatable distal operativeelements 198 and 200 respectively comprise ablation elements, such as,e.g., electrodes, for performing ablation therapy. A more detaileddescription of ablation electrodes is provided in Swanson et al., U.S.Pat. No. 5,582,609, which is fully incorporated herein by reference.First and second ablation elements 198 and 200 are fixed to the outersurface of the catheter body 192 by known methods, such as, e.g.,mechanical interference. Alternatively, first and second ablationelements 198 and 200 may be any conductor used to establish electricalcontact with a nonmetallic portion of a circuit, such as, e.g.,conductive ink, the manufacture of which is described in copendingapplication Ser. No. 08/879,343, filed Jun. 20, 1997, which is fullyincorporated herein by reference. In alternative embodiments, the firstand second non-rotatable distal operative elements 198 and 200respectively comprise diagnostic elements, such as, e.g., mapping orpacing electrodes.

The first non-rotatable proximal element 202 comprises a source ofenergy for the respective first and second ablation elements 198 and200. The source of energy may include, e.g., an RF energy generator suchas those described in Jackson et al., U.S. Pat. No. 5,383,874 andEdwards et al., U.S. Pat. No. 5,456,682, which are fully incorporatedherein by reference. It can be appreciated that the ablation elements198 and 200 can be individually energized with two separate sources ofenergy without straying from the principles taught by this invention. Itcan also be appreciated that the respective non-rotatable distalelements 198 and 200 and the first non-rotatable proximal element 202are not limited to ablation elements and a source of energy,respectively, but can, without straying from the principles taught bythis invention, respectively comprise any non-rotatable devices that arein electrical communications with one another. For example, thenon-rotatable distal elements 198 and 200 and the first non-rotatableproximal element 202 may respectively comprises mapping or pacingelectrodes and a signal generator.

The RF generator 202 is electrically coupled to the ablation elements198 and 200 through respective first and second transmission lines 208and 210. Each of the respective transmission lines 208 and 210preferably comprises a pair of lead wires, which are connected inparallel to the respective ablation elements 198 and 200. Various wireconnection techniques are described in U.S. Pat. No. 5,582,609, whichhas previously been expressly incorporated herein by reference. Therespective transmission lines 208 and 210 are embedded within the wallof the catheter body 192 using an extrusion process. It can beappreciated that the quantity of transmission lines that can be embeddedin the catheter body 192 is not limited to two. For instance, FIG. 11illustrates an alternative embodiment that employs four embeddedtransmission lines 212, 214, 216 and 218, which can be used to energizefour ablation elements.

As with the catheter assembly 150, the rotatable distal operativeelement 196 comprises an ultrasonic transducer element 220 with opposingmatching and backing layers 222 and 224, respectively. The transducerelement 220 is mounted in a transducer housing 226, which ismechanically and rotatably coupled to the drive unit 206 via the drivecable 194. The second proximal non-rotatable operative element 204comprises a transceiver, which is electrically coupled to the transducerelement 220 via a transmission line 228 disposed in the drive cable 194.

In use, the catheter assembly 190 is intravascularly inserted into apatient and maneuvered by the physician until a desired region of thepatient's coronary arteries is adjacent the transducer element 220. Withthe catheter assembly 190 properly positioned, ultrasonic imaging of theadjacent arterial tissue is performed to place the ablation elementsnext to abnormal tissue, such as, e.g., arythmic tissue. Arythmic tissuecan be located using mapping catheters, with the ultrasonic imagingbeing used to identify the mapping catheter electrodes next to theabnormal tissue. The physician can then place the respective ablationelements 198 and 200 adjacent the identified mapping catheterelectrodes, and thus the abnormal tissue. The RF generator 204 can thenbe operated to energize the respective ablation elements 198 and 200 viathe respective transmission lines 208 and 210, thereby ablating theabnormal tissue. The respective transmission lines 208 and 210 eclipsethe transducer element 220, thereby slightly reducing the imagingcapability of the catheter assembly 190.

Referring to FIGS. 14A and 14B, a sixth exemplary catheter assembly 230is provided for providing ultrasonic imaging of the vessel wall. Thecatheter assembly 230 generally includes an elongate catheter body 232,a plurality of distal operative elements 234 and a proximal operativeelement 236 coupled to the plurality of distal operative elements 234.

In particular, the plurality of distal operative elements 234respectively comprise transducer elements embedded in the distal end ofthe catheter body 232 and circumferentially arranged therearound to forma phased array. For ease of illustration, a limited number of transducerelements are shown. A phased array is normally made up of many moretransducer elements (typically 32 transducer elements). A more detaileddescription of the structure and utility of phased arrays is provided inBom, U.S. Pat. No. 3,938,502, which is expressly and fully incorporatedherein by reference.

The proximal operative element 236 comprises a transceiver, which iselectrically coupled to the plurality of transducer elements 234 viarespective transmission lines 236 (shown partially in phantom). Thetransceiver is configured to respectively provide a plurality of phasedelectrical signals to the respective transducer elements 232. Thetransmission lines 236 are embedded within the wall of the catheter body232 using an extrusion process. The catheter body 232 includes a guidewire lumen 238 formed therethrough to provide over-the-wire guiding ofthe catheter body 232 to the imaging region.

Many of the features described with respect to the catheter assemblies10, 60, 120, 150 and 190 can be variously combined to produce furtherembodiments. For example, ablation elements with correspondingtransmission lines and an RF generator can be added to the respectivecatheter assemblies 10, 60, 120, 150, and 230 to provide ablationtherapy capability. A forward looking transducer element can be added tothe catheter assembly 190, either installed on the front of the housing226 or embedded in the catheter body 192 to provide Doppler measurementsof the blood flow. Catheter assemblies 150 and 190 can be manufacturedexclusive of the rotatable transducer element to solely provide Dopplermeasurements of the blood flow or ablation therapy, respectively.

The number of transmission lines that can be embedded in the wall of theguide sheath, and thus the number of distal operative elements supportedby a particular catheter assembly, is limited by space availability andimpedance matching. In determining the characteristic impedance of theembedded transmission lines, the distance between the two wires, and thediameter of the wires of the transmission line must be taken intoaccount. In general, the characteristic impedance of the transmissionline is inversely proportional to the natural log of the distancebetween the two wires of the transmission line. Thus, the spacingbetween the respective wires for a given diameter of wires of embeddedtransmission lines should be chosen in a manner consistent with thedesired impedance levels of the respective transmission lines.

1. A catheter assembly, comprising: an elongate catheter body having aproximal end and a distal end; a drive cable disposed in the catheter,the drive cable having a proximal end and a distal end, and rotatablerelative to the catheter body; an operative element disposed on thedistal end of the drive cable, the operative element having a capacitivereactance at an operating frequency; a conductor having a proximal endand a distal end; and an inductive coupler disposed in the distal end ofthe catheter body and electrically coupled to the operative element andthe distal end of the conductor, wherein the inductive couplerinductively couples the operative element to the conductor and theinductive coupler has an inductive reactance that is substantially equalto the capacitive reactance at the operating frequency.
 2. The catheterassembly of claim 1, wherein the operative element comprises anultrasonic transducer.
 3. The catheter assembly of claim 1, wherein theconductor is disposed within the catheter body.
 4. The catheter assemblyof claim 1, wherein the inductive coupler comprises a stator fixablydisposed in the catheter body and electrically coupled to the distal endof the conductor, the stator comprising a generally hollow cylinder; anda rotor mechanically coupled to the distal end of the drive cable andelectrically coupled to the operative element, the rotor comprising arod rotatably disposed in the hollow cylinder.
 5. The catheter assemblyof claim 4, wherein the stator further comprises a first electricallyconductive coil disposed on the inner surface of the hollow cylinder,and the rotor further comprises a second electrically conductive coildisposed on the outer surface of the rod.
 6. The catheter assembly ofclaim 5, wherein the stator and rotor having opposing surface areas,wherein the respective stator and rotor surface areas, along with therespective diameter, size and number of turns of the first and secondelectrically conductive coils, are selected such that the value of theinductive reactance of the inductive coupler is substantially equal tothe capacitive reactance at the operating frequency.
 7. The catheterassembly of claim 4, wherein the stator has a first electricallyconductive coil; the rotator has a second electrically conductive coil,and the ratio of turns between the first and second electricallyconductive coils is selected such that the input impedance looking intothe inductive coupler from the conductor substantially matches thecharacteristic impedance of the conductor.
 8. A catheter assembly,comprising: an elongate catheter body having a proximal end and a distalend; a drive cable disposed in the catheter, the drive cable having aproximal end and a distal end, and rotatable relative to the catheterbody; first and second operative elements disposed on the distal end ofthe drive cable; first and second conductors, each conductor having aproximal end and a distal end; a first inductive coupler disposed in thedistal end of the catheter body and electrically coupled to the firstoperative element and the distal end of the first conductor, wherein thefirst inductive coupler inductively couples the first operative elementto the first conductor, the first inductive coupler comprising: a firststator fixably disposed in the catheter body and electrically coupled tothe distal end of the first conductor, the first stator comprising afirst generally hollow cylinder; a first rotor mechanically coupled tothe distal end of the drive cable and electrically coupled to the firstoperative element, the first rotor comprising a first rod rotatablydisposed in the first hollow cylinder; and a second inductive couplerdisposed in the distal end of the catheter body and electrically coupledto the second operative element and the distal end of the secondconductor, wherein the second inductive coupler inductively couples thesecond operative element to the second conductor, the second inductivecoupler comprising: a second stator fixably disposed in the catheterbody and electrically coupled to the distal end of the second conductor,the second stator comprising a second generally hollow cylinder; and asecond rotor mechanically coupled to the distal end of the drive cableand electrically coupled to the second operative element, the secondrotor comprising a second rod rotatably disposed in the second hollowcylinder.
 9. The catheter assembly of claim 8, wherein the first andsecond operative elements comprise ultrasonic transducers.
 10. Thecatheter assembly of claim 9, wherein the catheter body defines an axis,the first operative element is configured to transmit ultrasonic wavespropagating in a direction axially aligned with the catheter body, andthe second operative element is configured to transmit ultrasonic wavespropagating in a direction at a selected angle relative to the catheterbody axis.
 11. The catheter assembly of claim 8, wherein the first andsecond conductors are disposed within the catheter body.
 12. Thecatheter assembly of claim 8, wherein the first stator further comprisesa first electrically conductive coil disposed on the inner surface ofthe first hollow cylinder, the first rotor further comprises a secondelectrically conductive coil disposed on the outer surface of the firstrod, the second stator further comprises a third electrically conductivecoil disposed on the inner surface of the second hollow cylinder, andthe second rotor further comprises a fourth electrically conductive coildisposed on the outer surface of the second rod.
 13. The catheterassembly of claim 8, wherein the first inductive coupler is electricallyisolated from the second inductive coupler.
 14. The catheter assembly ofclaim 13, further comprising an isolation disk disposed in the catheterbody between the first and second inductive couplers.
 15. A catheterassembly, comprising: a main catheter body having a proximal end and adistal end; a telescoping catheter body movably disposed in the maincatheter body, the telescoping catheter body having a proximal end and adistal end; a drive cable disposed in the telescoping catheter, thedrive cable having a proximal end and a distal end, and rotatablerelative to the telescoping catheter body, an operative element disposedon the distal end of the drive cable; a conductor having a proximal endand a distal end; and an inductive coupler disposed in the distal end ofthe telescoping catheter body and electrically coupled to the operativeelement and the distal end of the conductor, wherein the inductivecoupler inductively couples the operative element to the conductor, theinductive coupler comprising: a stator fixably disposed in thetelescoping catheter body and electrically coupled to the distal end ofthe conductor, the stator comprising a generally hollow cylinder; and arotor mechanically coupled to the distal end of the drive cable andelectrically coupled to the operative element, the rotor comprising arod rotatably disposed in the hollow cylinder.
 16. The catheter assemblyof claim 15, wherein the operative element is an ultrasonic transducer.17. The catheter assembly of claim 15, wherein the operative element isdisposed in the main catheter body distal to the telescoping catheterbody.
 18. The catheter assembly of claim 15, wherein the conductor isdisposed in the telescoping catheter body.
 19. A catheter assembly,comprising: an elongate catheter body having a proximal end and a distalend; a drive cable disposed in the catheter, the drive cable having aproximal end and a distal end, and rotatable relative to the catheterbody; an operative element disposed on the distal end of the drivecable; a conductor having a proximal end and a distal end; and aninductive coupler disposed in the distal end of the catheter body andelectrically coupled to the operative element and the distal end of theconductor, wherein the inductive coupler inductively couples theoperative element to the conductor, the inductive coupler comprising: astator fixably disposed in the catheter body and electrically coupled tothe distal end of the conductor, the stator comprising a generallyhollow cylinder; and a rotor mechanically coupled to the distal end ofthe drive cable and electrically coupled to the operative element, therotor comprising a rod rotatably disposed in the hollow cylinder. 20.The catheter assembly of claim 19, wherein the operative elementcomprises an ultrasonic transducer.
 21. The catheter assembly of claim19, wherein the conductor is disposed within the catheter body.
 22. Thecatheter assembly of claim 19, wherein the stator further comprises afirst electrically conductive coil disposed on the inner surface of thehollow cylinder, and the rotor further comprises a second electricallyconductive coil disposed on the outer surface of the rod.
 23. Thecatheter assembly of claim 22, wherein the operative element has acapacitive reactance at an operating frequency, the stator and rotorhaving opposing surface areas, wherein the respective stator and rotorsurface areas, along with the respective diameter, size and number ofturns of the first and second electrically conductive coils, areselected such that the value of the inductive reactance of the inductivecoupler is substantially equal to the capacitive reactance at theoperating frequency.
 24. The catheter assembly of claim 19, wherein thestator has a first electrically conductive coil; the rotator has asecond electrically conductive coil, and the ratio of turns between thefirst and second electrically conductive coils is selected such that theinput impedance looking into the inductive coupler from the conductorsubstantially matches the characteristic impedance of the conductor.